According to the guidance notes, the courier address is

Immigration & Nationality Directorate
Work Permits (UK) HSMP
7th floor
Fountain Precinct
Balm Green
Sheffield
S1 2JA

Good luck!

Hi - I'm thinking about applying for HSMP. I have been a full-time university student for almost 12 years now (BSc, MSc, PhD almost done, broadly within mathematical and physical sciences, with a good deal of computational work thrown in). Unfortunately as time has slipped by I've become too old to ...